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      Simulations of symptomatic treatments for Alzheimer's disease: computational analysis of pathology and mechanisms of drug action

      , 1 , 2 , 2 , 2

      Alzheimer's Research & Therapy

      BioMed Central

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          A substantial number of therapeutic drugs for Alzheimer's disease (AD) have failed in late-stage trials, highlighting the translational disconnect with pathology-based animal models.


          To bridge the gap between preclinical animal models and clinical outcomes, we implemented a conductance-based computational model of cortical circuitry to simulate working memory as a measure for cognitive function. The model was initially calibrated using preclinical data on receptor pharmacology of catecholamine and cholinergic neurotransmitters. The pathology of AD was subsequently implemented as synaptic and neuronal loss and a decrease in cholinergic tone. The model was further calibrated with clinical Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-Cog) results on acetylcholinesterase inhibitors and 5-HT6 antagonists to improve the model's prediction of clinical outcomes.


          As an independent validation, we reproduced clinical data for apolipoprotein E (APOE) genotypes showing that the ApoE4 genotype reduces the network performance much more in mild cognitive impairment conditions than at later stages of AD pathology. We then demonstrated the differential effect of memantine, an N-Methyl-D-aspartic acid (NMDA) subunit selective weak inhibitor, in early and late AD pathology, and show that inhibition of the NMDA receptor NR2C/NR2D subunits located on inhibitory interneurons compensates for the greater excitatory decline observed with pathology.


          This quantitative systems pharmacology approach is shown to be complementary to traditional animal models, with the potential to assess potential off-target effects, the consequences of pharmacologically active human metabolites, the effect of comedications, and the impact of a small number of well described genotypes.

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          Most cited references 86

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          Gene dose of apolipoprotein E type 4 allele and the risk of Alzheimer's disease in late onset families.

          The apolipoprotein E type 4 allele (APOE-epsilon 4) is genetically associated with the common late onset familial and sporadic forms of Alzheimer's disease (AD). Risk for AD increased from 20% to 90% and mean age at onset decreased from 84 to 68 years with increasing number of APOE-epsilon 4 alleles in 42 families with late onset AD. Thus APOE-epsilon 4 gene dose is a major risk factor for late onset AD and, in these families, homozygosity for APOE-epsilon 4 was virtually sufficient to cause AD by age 80.
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            Developmental and regional expression in the rat brain and functional properties of four NMDA receptors.

            An in situ study of mRNAs encoding NMDA receptor subunits in the developing rat CNS revealed that, at all stages, the NR1 gene is expressed in virtually all neurons, whereas the four NR2 transcripts display distinct expression patterns. NR2B and NR2D mRNAs occur prenatally, whereas NR2A and NR2C mRNAs are first detected near birth. All transcripts except NR2D peak around P20. NR2D mRNA, present mainly in midbrain structures, peaks around P7 and thereafter decreases to adult levels. Postnatally, NR2B and NR2C transcript levels change in opposite directions in the cerebellar internal granule cell layer. In the adult hippocampus, NR2A and NR2B mRNAs are prominent in CA1 and CA3 pyramidal cells, but NR2C and NR2D mRNAs occur in different subsets of interneurons. Recombinant binary NR1-NR2 channels show comparable Ca2+ permeabilities, but marked differences in voltage-dependent Mg2+ block and in offset decay time constants. Thus, the distinct expression profiles and functional properties of NR2 subunits provide a basis for NMDA channel heterogeneity in the brain.
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              How inhibition shapes cortical activity.

              Cortical processing reflects the interplay of synaptic excitation and synaptic inhibition. Rapidly accumulating evidence is highlighting the crucial role of inhibition in shaping spontaneous and sensory-evoked cortical activity and thus underscores how a better knowledge of inhibitory circuits is necessary for our understanding of cortical function. We discuss current views of how inhibition regulates the function of cortical neurons and point to a number of important open questions. Copyright © 2011 Elsevier Inc. All rights reserved.

                Author and article information

                Alzheimers Res Ther
                Alzheimers Res Ther
                Alzheimer's Research & Therapy
                BioMed Central
                26 November 2012
                : 4
                : 6
                : 50
                [1 ]Department of Biomedical Engineering, Oregon Health & Science University, 3303 SW Bond Avenue, Portland, OR 97239 USA
                [2 ]In Silico Biosciences, Inc., 405 Waltham Street, Lexington, MA 02421 USA
                Copyright ©2012 Roberts et al.

                This is an open access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.




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